KR101269657B1 - A piston-and-cylinder assembly with a variable diametral clearance and a cylinder for use in a piston-and-cylinder assembly with a variable diametral clearance - Google Patents

Abstract

A piston-and-cylinder assembly, used in cooling sys terns that may include, for example, refrigerators, air-conditioning systems and the like. In order to solve the problems of volumetric loss (or of cooling capacity) of compressors in general, according to the present invention, one foresees configuring the cylinder (11) of the compression chamber in such a manner that the friction will be as low as possible in the phase in which the gas being compresses still does not exert a significant force onto the piston (10) top and will only have a significant effect during the phase in which the gas to be compressed exerts a greater force onto the piston (10), a moment when the volumetric loss impairs the efficiency of the compressor.

Description

PISTON-AND-CYLINDER ASSEMBLY WITH A VARIABLE DIAMETRAL CLEARANCE, AND A CYLINDER FOR USE IN A PISTON- AND-CYLINDER ASSEMBLY WITH A VARIABLE DIAMETRAL CLEARANCE}

The present invention relates to a piston and cylinder assembly as well as to a compression cylinder, and more particularly to the application to alternating compressors used in cooling systems which may include, for example, refrigerators, air conditioning systems and the like. The disclosure of the present invention may also be applied generally to motors using reciprocating cylinders, such as linear compressors and internal combustion engines.

This application claims the priority of Brazilian Patent Case No. PI0503019-6, filed July 22, 2005, which is incorporated herein by reference.

As is known in the art and as can be seen in FIG. 1, in the reciprocating piston compressor 1 used for cooling, the compression of the cooling gas is carried out by the minimum and provided by the drive mechanism, respectively called bottom dead center and top dead center. Between maximal displacements is achieved through reciprocation of the piston 10 in the cylinder 11 (which constitutes a compression chamber C of varying sizes). The compression chamber is open at one end and closed at the other end by the valve plate 5. There must be a difference between the diameters of the piston and the compression chamber in order for the movement of the piston 10 to take place in an appropriate manner. In the presently known compressor 1, the diameter of the piston and the diameter of the compression chamber remain constant, characterized by a gap F of constant or constant diameter.

During operation of the compressor, the gap existing between the piston and the compression chamber remains filled with lubricating oil, providing bearing support to the piston 10 and thus the wall of the compression chamber resulting in wear of the piston 10 and / or the compression chamber. Contact with is prevented. This is due to the loss of mechanical energy to overcome the viscous friction provided by the oil and by the relative movement of the piston with respect to the compression chamber.

When the piston 10 moves from the bottom dead center to the top dead center, the gas present inside the compression chamber is compressed and the pressure increases with respect to the gas pressure present in the compressor housing. This creates a pressure difference that tends to release a portion of the gas to be compressed into the housing, which then leaks through the gap F in diameter. This phenomenon is characterized by the loss of volume (or loss of cooling capacity) of the compressor, as the compression work is done on the gas lost through leaking. This loss directly reduces the energy efficiency of the compressor.

The loss of mechanical energy and leakage of gas through the gap present between the piston and the compression chamber is strongly influenced by the value of this gap, the smaller the value, the greater the loss of mechanical energy and the less leakage of gas. On the other hand, the larger the value, the less the loss of mechanical energy and the greater the leakage of gas. For this reason, high-efficiency compressors seek to obtain a gap value at which gas leakage and loss of mechanical energy will be optimal so that the compressor's energy efficiency is maximized.

In addition to the diameter gap F between the piston and the compression chamber, the following factors affect the loss of mechanical energy and the leakage of gas.

Iii) diameter of piston (10)

Ii) the compression chamber and the length of the piston 10

Iii) the distance the piston 10 has moved

Ⅳ) rotation speed of drive shaft

Iii) the structure of the drive mechanism

Iii) the type of cooling gas used

Iii) the type of lubricant, and

Iii) operating conditions (pressure and temperature) of the compressor;

The compressor has a moment when the volume loss is at its maximum. This can be observed in Figure 2, which shows the position of the piston moving between the bottom dead center LDP and the top dead center UDP.

As shown, between displacements from bottom dead center to top dead center, the volume loss between crank angles between 0 ° and 125 ° is negligible. The same thing happens in the opposite direction: when the piston moves from the top dead center to the bottom dead center, the volume loss is negligible from 210 ° to 360 ° and a new rotation cycle of the crank begins. However, between 125 ° and 210 ° angles (or leakage area LeR), the volume loss increases considerably and thus measures must be taken to prevent low efficiency when the piston 10 is extended.

To solve this problem, one known in the art is described in German patent document DE 236148, which discloses the use of a piston and cylinder assembly with a variable diameter gap. This document discloses a cylinder in which half of the piston stroke has a constant diameter gap and the other half of the piston stroke has a diameter gap which decreases constantly to the bottom dead center. Despite improving the problem of gas leakage in the leak zone LeRR, the upper part of the piston needs to be specially formed, so that the gap between the diameters does not decrease excessively close to the top dead center (UDP), thereby increasing the friction. As a result, piston fatigue occurs as well as loss of efficiency of the compressor. In this way, although the solution described in this document reduces gas loss in the leak zone (LeaR), the piston needs to be manufactured with differentiated properties, thus increasing the manufacturing cost of the piston and cylinder assembly.

Another conventional solution is known from patent document WO 94/24436. This document discloses a cylindrical profile formed in the shape of a conical cut out top, where the cylinder diameter at the top dead center (UDP) is smaller than the diameter of the cylinder 11 at the bottom dead center (LDP) so that the gap in diameter increases the pressure inside the compression chamber. Bring it. This solution does not show high efficiency despite the possibility of more precise sealing of the cylinder, since the pressure in the compression chamber rises significantly only in the region closer to the top dead center.

In order to solve the problem of the volume loss (or cooling capacity loss) of the compressor (or similar device), according to the invention, the frictional gas is made as small as possible without applying a significant force on the piston 10 and The cylinder 11 of the compression chamber is formed such that the friction has a significant effect only while the gas to be compressed exerts a greater force on the piston 10, at which moment the volume loss impairs the efficiency of the compressor.

Thus, the present invention is based on the fact that the leakage of gas through the gap present between the piston and the compression chamber is a function of the gas pressure difference inside the compression chamber and the housing (not shown). Since a large pressure increase inside the compression chamber occurs only when the piston is close to top dead center, gas leakage occurs only at the final compression moment. Thus, it is concluded that the gap of the diameter existing between the piston and the compression chamber should be small only when the piston approaches top dead center. In this way, the leakage of gas through the gap existing between the piston and the compression chamber will be kept small by the fact that the gap between the diameters reduces the pressure between the compression chamber and the pressure inside the housing in a significant area. At most of the length, the clearance of the diameter existing between the piston and the compression chamber will be large and thus the friction will be small, resulting in less loss of mechanical energy.

The objectives of the present invention are that the piston is displaceably positioned inside the cylinder, the cylinder has a compression chamber, the piston moves between the top dead center and the bottom dead center, and the diameter gap separates the sliding surface of the piston from the cylinder guide surface and The cylinder guide surface is achieved by the piston and cylinder assembly, formed such that the gap in diameter can vary along the displacement of the piston from the bottom dead center to the top dead center. These objects are also achieved by the fact that the fluctuation of the diameter gap along the displacement of the piston is nonlinear, in one embodiment the cylinder sliding surface is the first displacement in the cylindrical profile and the second displacement in the truncated cone profile. Wherein the first displacement extension is located close to top dead center, and in another embodiment the cylinder has a first displacement extension in the truncated cone profile and a second displacement extension in the truncated cone profile, The first displacement extension is located near the top dead center, the diameter of the cylinder at the top dead center is smaller than the diameter of the cylinder at the bottom dead center, and the cylinder diameter and the top dead center toward the bottom dead center at the first displacement extension. The relationship of the cylinder diameter toward is different from the relationship between the cylinder diameter toward the bottom dead center and the cylinder diameter toward the top dead center at the second displacement extension portion.

And the objects of the present invention have a profile with a smaller and variable diameter close to the end of the stroke, the variation of the diameter being achieved by a cylinder for use in a piston and cylinder assembly which is non-linear. This cylinder has a first displacement extension in the cylindrical profile and a second displacement extension in the truncated cone profile, or a first displacement extension in the truncated cone profile and a second in the truncated cone profile. It has a displacement extension, and the angle of the second displacement extension is more open than the angle of the first displacement extension.
Within the possibility that the gas to be compressed has this diameter variation proportional to the force exerted on the piston, the cylindrical profile with the piston approaching its maximum at top dead center, which prevents volume loss, and (the Combination of stretch in the truncated cone profile); A combination of two cone profiles that reduce the gap in diameter and thus prevent volume loss, the cone closest to top dead center with a more closed angle; Or it can be expected that the cylindrical profile is non-linear and formed so as to reduce the diameter gap in a manner inversely proportional to the pressure the gas exerts on the piston.

The present invention is described in detail with reference to the drawings below.

1 is a schematic view showing a compression chamber of a reciprocating compressor according to the prior art.

2 is a graph showing the relationship between the position of the piston and the gas leak through the gap existing between the piston and the compression chamber as a function of crank angle.

Figure 3 is a schematic diagram showing a conical shaped compression chamber cut in two tops according to the present invention.

Fig. 4 is a schematic view of a compression chamber having one ton portion in the shape of two truncated cones according to another embodiment of the present invention, wherein the portion close to the top dead center (UDP) is cylindrical.

As shown in Figures 3 and 4, the piston and cylinder assembly are arranged in such a way that the piston 10 is displaceably positioned inside the cylinder 11. The cylinder 11 has a compression chamber C. The compression chamber C changes between the minimum volume when the piston 10 is displaced to top dead center UDP and the maximum volume when the piston is at bottom dead center LDP. The gap F of the diameter separates the piston sliding surface 9 (outer side of the piston 10) and the cylinder guide surface 12 (inner side of the cylinder 11).

In order to achieve the objects of the present invention, the sliding surface 9 of the cylinder 11 is formed in such a manner that the gap F of diameter varies along the displacement of the piston 10 between the top dead center UDP and the bottom dead center LDP. Formed, this change can be linear or nonlinear.

One of the embodiments of the present invention is shown in FIG. 4, aiming to bring the gap F of diameter close to the aspect of volume loss shown in FIG. 2. According to this embodiment, the compression chamber has a first displacement extension LR in the cylindrical profile of the sliding surface 9 of the cylinder 10 and a second displacement extension LC in the conical profile cut off the top. The first displacement extension LR is located close to the top dead center (UDP). As shown in Figure 4, the diameter of the truncated cone profile is minimal close to the top dead center (UDP), more specifically the minimum at the start of the displacement extension (LR) in the cylindrical profile and the bottom dead center (LDP). Is at max.

Thus, the gap F of the diameter existing between the piston and the compression chamber is minimal and close to a constant top dead center (UDP), and the gap can vary at each position of the piston 10 and at bottom dead center LDP There will be an area that is maximum.

According to another embodiment of the present invention, as shown in Fig. 3, the cylinder 11 has a first displacement extension LR in the truncated cone profile and a second displacement extension in the truncated cone profile as well. It may be formed to have a portion LC, where the first displacement extension portion LR is located close to the top dead center (UDP). In the present embodiment, the diameter of the cylinder 11 at the top dead center UDP is larger than the diameter of the cylinder 11 at the bottom dead center LDP. Preferably, the angle of the cone cut out of the top of the second displacement extension LC is more open than the angle of the first displacement extension LR, so that the bottom dead center LDP at the first displacement extension LR is The relationship between the diameter of the cylinder 11 at the top dead center UDP is determined by the relationship between the bottom dead center LDP at the second displacement extension LC and the diameter of the cylinder 11 at the top dead center UDP. Has different results.

In other words, the relationship between the diameter of the cylinder toward the bottom dead center LDP in the first displacement extension portion LR and the diameter of the cylinder 11 at the top dead center UDP is determined by the second displacement extension LC. It is larger than the relationship between the diameter of the cylinder at the bottom dead center LDP and the diameter of the cylinder 11 toward the top dead center UDP.

The case where the profile of the cylinder 11 is non-linear and is formed to reduce the gap of the diameter in a manner inversely proportional to the pressure exerted by the gas by the gas is not shown in the figure but as shown in FIG. It should have a sliding surface that is adjusted to the aspect of the leak. Necessary modifications must be made for each particular solution of the piston and cylinder assembly to which the present disclosure is to be applied.

For all the embodiments described, it is achievable for the purpose of the present invention to provide a minimum displacement resistance and at the same time to prevent leakage of compressed gas so that the diameter gap is adjusted to follow the sun of the gas in the pressure chamber C. Thus the disadvantages of the prior art are overcome.

Having described the preferred embodiments above, the scope of the present invention is not limited to the content of the appended claims as encompassing other possible variables, and includes possible equivalents.

Claims (11)

Piston and cylinder assembly, The piston 10 is displaceably positioned inside the cylinder 11, The cylinder 11 has a compression chamber C, The piston 10 moves between the top dead center (UDP) and the bottom dead center (LDP), A gap F of diameter separates the piston 10 sliding surface 9 and the cylinder 11 guide surface 12, The cylinder (11) guide surface (12) is a piston and cylinder assembly in which the diameter gap (F) is formed to change along the displacement of the piston (10) assembly. The gap F of the diameter changes from the bottom dead center LDP to the top dead center UDP, The sliding surface 9 of the cylinder 11 has a first displacement extension portion LR and a second displacement extension portion LC positioned close to the top dead center UDP, and the first displacement extension portion LR. Has a cylindrical profile and the second displacement extension LC has a truncated cone profile, the diameter of the truncated cone being closer to the bottom dead center (LDP) and larger than the diameter closer to the top dead center (LDP). A piston and cylinder assembly, characterized in that. delete delete 2. A piston and cylinder assembly according to claim 1, wherein the gap (F) of the diameter of the first displacement extension (LR) in the cylindrical profile is minimal. The piston and cylinder assembly of claim 1, wherein the topped cone profile has a diameter close to top dead center (UDP) and maximum at bottom dead center (LDP). 2. The cylinder (11) according to claim 1, wherein the cylinder (11) has a first displacement extension (LR) in the truncated cone profile and a second displacement extension (LC) in the truncated cone profile. The unit LR is located near the top dead center UDP, The diameter of the cylinder 11 at the top dead center UDP is larger than the diameter of the cylinder 11 at the bottom dead center LDP, The relationship between the diameter of the cylinder 11 at the bottom dead center LDP at the first displacement extension part LR and the diameter of the cylinder 11 at the top dead center UDP is the bottom dead center LDP at the second displacement extension LC. And a relationship between the diameter of the cylinder on the side) and the diameter of the cylinder on the top dead center (UDP) side. The bottom dead center LDP at the second displacement extension LC is defined as a relation between the cylinder diameter at the bottom dead center LDP side and the top dead center UDP side in the first displacement extension part LR. And a relationship between the diameter of the cylinder (11) at the top dead center (UDP) side. 2. A piston and cylinder assembly according to claim 1, wherein the gap (F) in diameter is proportional to the force exerted on the piston (10) by the gas to be compressed in the compression chamber (C). At the end of the stroke there is a profile with a smaller and variable diameter, the variation of the diameter being a cylinder for use in nonlinear piston and cylinder assemblies, the first displacement extension LR and the second displacement extension LC And a second displacement extension (LC) has a conical profile with a truncated top. 10. A cylinder according to claim 9, having a first displacement extension (LR) in the cylindrical profile. The angle of the second displacement extension LC according to claim 9, having a first displacement extension LR in the truncated cone profile and a second displacement extension LC in the truncated cone profile. The cylinder, characterized in that more open than the angle of the first displacement extension (LR).

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